Choose a version:
53% The original file has 67155 bytes (65.6k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 35601 bytes (34.8k, 53%).

After GZIP compression these minified files vary in size:
Microsoft
  12274 bytes (12.0k)
CDN, direct link
Boot
  11326 bytes (11.1k)
CDN, direct link
MaxCDN
  11326 bytes (11.1k)
CDN, direct link
cdnjs
  9524 bytes (9.3k)
CDN, direct link
gzip -6 (default)
  9464 bytes (9.2k)
local copy
cdnhttps
  9441 bytes (9.2k)
CDN, direct link
gzip -9
  9432 bytes (9.2k)
local copy
unpkg
  9426 bytes (9.2k)
CDN, direct link
Yandex
  9412 bytes (9.2k)
CDN, direct link
jsdelivr
  9412 bytes (9.2k)
CDN, direct link
7zip -mx=9 -tgzip
  9123 bytes (8.9k)
local copy
libdeflate -12
  9117 bytes (8.9k)
local copy
kzip -s0 -rn -b2
  9109 bytes (8.9k)
local copy
pigz -11 -n
  9065 bytes (8.9k)
local copy
Zopfli
  9058 bytes (8.8k)
local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/bootstrap/bootstrap-3.3.1.min.js

You will automatically get the smallest Bootstrap 3.3.1 file, ETag caching is available and
if your browser doesn't support GZIP decompression then the uncompressed version will be sent.

Currently best Zopfli settings

Save 354 bytes by using my Bootstrap 3.3.1 Zopfli version instead of the best available CDN (3.91% smaller than jsdelivr, 9058 vs. 9412 bytes):
You can use my super-compressed files for whatever purpose you like as long as you respect the library's original license agreement.
There are no restrictions from my side - but please avoid hot-linking if you run a high-traffic website.

These command-line settings yielded the best compression ratio so far (Linux version of zopfli-krzymod):
zopfli --i1000000 --mb8 --mls4 --bsr18 --lazy --ohh

(found February 26, 2016)
Description Value Parameter
iterations 1000000  --i1000000
maximum blocks 8  --mb8
maximum length score 4  --mls4
block splitting recursion 18  --bsr18
lazy matching in LZ77 yes  --lazy
optimized Huffman headers yes  --ohh
initial random W for iterations 1  --rw1
initial random Z for iterations 2  --rz2

Verify file integrity

After decompression, my uncompressed files are identical to the original ones:

MD5:
curl --silent --compressed https://raw.githubusercontent.com/twbs/bootstrap/v3.3.1/dist/js/bootstrap.min.js --location | md5sum
2616d3564578d8f845813483352802a9  -
curl --silent --compressed http://minime.stephan-brumme.com/files/bootstrap/bootstrap-3.3.1.min.zopfli.js.gz | md5sum
2616d3564578d8f845813483352802a9  -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/twbs/bootstrap/v3.3.1/dist/js/bootstrap.min.js --location | sha1sum
5ada7c103fc1deabc925cc1fdbbb6e451c21fc70  -
curl --silent --compressed http://minime.stephan-brumme.com/files/bootstrap/bootstrap-3.3.1.min.zopfli.js.gz | sha1sum
5ada7c103fc1deabc925cc1fdbbb6e451c21fc70  -

All listed CDNs deliver identical contents:
CDN Size (compressed) MD5 (uncompressed) Timestamp
Microsoft 12274 bytes 2616d3564578d8f845813483352802a9 (invalid)
Boot 11326 bytes 2616d3564578d8f845813483352802a9 (invalid)
MaxCDN 11326 bytes 2616d3564578d8f845813483352802a9 (invalid)
cdnjs 9524 bytes 2616d3564578d8f845813483352802a9 (invalid)
cdnhttps 9441 bytes 2616d3564578d8f845813483352802a9 December 24, 2015 @ 07:36
unpkg 9426 bytes 2616d3564578d8f845813483352802a9 July 11, 2016 @ 16:21
Yandex 9412 bytes 2616d3564578d8f845813483352802a9 (invalid)
jsdelivr 9412 bytes 2616d3564578d8f845813483352802a9 (invalid)

Note: only the MD5 hashes are shown to keep things simple.

Other Versions

Available Bootstrap versions at minime.stephan-brumme.com:

3.3.7, 3.3.6, 3.3.5, 3.3.4, 3.3.2, 3.3.1, 3.3.0,
3.2.0,
3.1.1, 3.1.0,
3.0.3, 3.0.2, 3.0.1, 3.0.0

The project site contains an overview how well these versions were compressed.
Other interesting projects are AngularJS, BackboneJS, D3, Dojo, Ember, jQuery, Knockout, lodash, React, Socket.IO, ThreeJS, UnderscoreJS and Vue.

Changelog

Best Zopfli parameters so far:
Size Improvement Parameters Found
9058 bytes -1 byte zopfli --i1000000 --mls4 --bsr18 --lazy --ohh February 26, 2016 @ 12:38
9059 bytes -1 byte zopfli --i100000 --mls4 --bsr18 --lazy --ohh September 25, 2015 @ 16:31
9060 bytes -1 byte zopfli --i10000 --mls4 --bsr18 --lazy --ohh September 25, 2015 @ 15:01
9061 bytes -1 byte zopfli --i10000 --mls512 --bsr12 --lazy --ohh September 10, 2015 @ 17:37
9062 bytes -2 bytes zopfli --i1000 --mls512 --bsr6 --lazy --ohh September 10, 2015 @ 16:36
9064 bytes zopfli --i100 --mls4096 --bsr16 --lazy --ohh September 10, 2015 @ 16:27

If there are multiple parameter sets yielding the same compressed size, only the first one found is shown.

Most recent activity on July 11, 2016 @ 16:21.

Heatmaps

This Zopfli heatmap visualizes how compression changes when modifying the --bsr and --mls parameter.
Cell's contents is the best filesize achieved (in bytes, hover with mouse over cells to see number of iterations).

Good parameters are green, bad are red. The best and worst are bold as well.
The brightness of the blue background color indicates how many iterations were processed:
10,000, 100,000 or 1,000,000.
bsr \ mls
2 4 8 16 32 64 128 256 512 1024 2048 4096 8192 16384 32768
bsr \ mls
2 4 8 16 32 64 128 256 512 1024 2048 4096 8192 16384 32768
9070 9070 9070 9070 9069 9070 9069 9068 9070 9071 9073 9072 9064 9069 9063
9061 9061 9062 9061 9062 9061 9061 9062 9062 9062 9061 9063 9064 9068 9065
9064 9064 9062 9063 9062 9064 9061 9062 9061 9061 9063 9061 9061 9064 9063
9058 9058 9061 9061 9062 9062 9061 9062 9061 9062 9064 9061 9064 9062 9068
9061 9061 9062 9061 9061 9061 9061 9062 9062 9062 9061 9061 9064 9068 9063
9060 9060 9062 9062 9062 9061 9061 9064 9062 9061 9061 9063 9063 9062 9063
9061 9061 9061 9061 9061 9062 9062 9061 9061 9062 9062 9065 9062 9068 9063
9058 9058 9061 9070 9062 9061 9062 9061 9062 9062 9062 9063 9061 9061 9064
9063 9063 9062 9061 9063 9061 9061 9062 9061 9061 9062 9061 9065 9063 9062
9060 9060 9062 9061 9062 9062 9062 9062 9062 9063 9062 9065 9064 9062 9064
9061 9061 9062 9062 9062 9062 9061 9062 9061 9061 9062 9065 9062 9069 9066
9061 9061 9061 9061 9062 9061 9061 9061 9062 9062 9064 9062 9061 9062 9065
9061 9061 9062 9061 9062 9061 9062 9063 9062 9061 9061 9061 9062 9069 9063
9060 9060 9061 9061 9061 9062 9061 9063 9062 9061 9062 9061 9061 9063 9063
9058 9058 9063 9061 9062 9062 9061 9061 9061 9061 9061 9065 9064 9062 9063
9058 9058 9062 9061 9062 9062 9061 9062 9062 9062 9062 9062 9061 9068 9068
9060 9060 9061 9061 9062 9062 9062 9062 9062 9061 9064 9061 9064 9062 9063
9060 9060 9061 9061 9062 9062 9062 9061 9062 9062 9061 9062 9064 9062 9062
9060 9060 9061 9061 9062 9061 9062 9061 9062 9062 9062 9061 9062 9062 9064
9060 9060 9062 9061 9062 9061 9061 9062 9062 9061 9064 9065 9061 9068 9063
9060 9060 9062 9061 9062 9062 9061 9062 9062 9061 9062 9062 9061 9068 9063
9061 9061 9062 9061 9062 9064 9062 9061 9062 9063 9062 9062 9063 9069 9063
9061 9061 9062 9061 9062 9061 9062 9062 9062 9061 9061 9061 9062 9062 9062

Due to the Monte Carlo design of my search algorithm, not all parameters have reached the same number of iterations yet:
Iterations Min. Bytes Reduction Coverage
100 9062 bytes 100%
1,000 9061 bytes -1 byte 100%
10,000 9060 bytes -1 byte 100%
100,000 9059 bytes -1 byte 6.96%
1,000,000 9058 bytes -1 byte 2.32%
10,000,000

KZIP has far less options available for tuning/optimization. I only played around with the number of blocks (parameter -n):
Blocks Min. Bytes Compared To Best Zopfli Compared To Best KZIP
9120 bytes +62 bytes (+0.68%) +11 bytes
9121 bytes +63 bytes (+0.70%) +12 bytes
9109 bytes +51 bytes (+0.56%)
9125 bytes +67 bytes (+0.74%) +16 bytes
9157 bytes +99 bytes (+1.09%) +48 bytes
9193 bytes +135 bytes (+1.49%) +84 bytes
9236 bytes +178 bytes (+1.97%) +127 bytes
9266 bytes +208 bytes (+2.30%) +157 bytes
9313 bytes +255 bytes (+2.82%) +204 bytes

Non-DEFLATE Algorithms

Archivers based on completely different compression algorithms often produce superior results.
Unfortunately, browsers only support gzip compression at the moment.
Algorithm Program Parameters Size Compared To Best Zopfli
RAR (proprietary) RAR rar a -m5 -md64m -mc63:128t -mt1 7546 bytes -1512 bytes (-16.69%)
ZPAQ (Wikipedia) zpaq zpaq -method 69 8237 bytes -821 bytes (-9.06%)
Brotli (Wikipedia) brotli brotli -q 11 8354 bytes -704 bytes (-7.77%)
PPMd (Wikipedia) 7zip 7za a -mx=9 -m0=ppmd 8601 bytes -457 bytes (-5.05%)
Burrows-Wheeler transform (Wikipedia) bzip2 bzip2 -9 8802 bytes -256 bytes (-2.83%)
LZMA2 (Wikipedia) xz xz -9 9020 bytes -38 bytes (-0.42%)
ZSTD (Wikipedia) zstd zstd -19 9075 bytes +17 bytes (+0.19%)

Detailled Analysis

I wrote a DEFLATE decoder in Javascript. Click the button below to start a client-side analysis of the smallest gzipped files (may take a second):


Notes: pigz is a fast open source multi-threaded implementation of gzip written by one of the original authors of gzip.
However, when using compression level 11, pigz actually switches to the slower Zopfli algorithm and isn't multi-threaded anymore.
KrzyMOD's extensions to Zopfli offer the highest level of configuration and is therefore used for my brute-force search.
Ken Silverman wrote the closed-source KZIP compression program and Jonathon Fowler ported it to Linux.
Defluff was created by Joachim Henke; DeflOpt is a tool by Ben Jos Walbeehm.

website made by Stephan Brumme in 2015 and still improving in 2017.
all timestamps are displayed in central european time. see my changelog.
no flash, not even images or external css files - and everything squeezed into a single html file.
which was handsomely compressed before releasing it into the wild internet - obviously.

please visit my homepage and my blog, too.
email: minime (at) stephan-brumme.com